1. Field of the Invention
This invention relates generally to a seal section for an electrical submersible pump. More particularly, the invention relates to a bellows in a seal section of an electrical submersible pump.
2. Background
Electrical submersible pumps (ESPs) have been used to lift fluid from bore holes, particularly for oil production. In operation, a pump of an electrical submersible pump is placed below the fluid level in the bore hole. The well fluid often contains corrosive compounds such as brine water, CO2, and H2S that can shorten the run life of an ESP when the ESP is submerged in the well fluid. Corrosion resistant units have been developed that have motors that utilize seals and barriers to exclude the corrosive agents from the internal mechanisms of the ESP.
A typical submersible pump has a motor, a pump above the motor, and a seal section between the motor and the pump. The seal section allows for expansion of the dielectric oil contained in the rotor gap of the motor. Temperature gradients resulting from an ambient and motor temperature rise cause the dielectric oil to expand. The expansion of the oil is accommodated by the seal section. Additionally, the seal section is provided to equalize the casing annulus pressure with the internal dielectric motor fluid. The equalization of pressure across the motor helps keep well fluid from leaking past sealed joints in the motor. It is important to keep well fluids away from the motor because well fluid that gets into the motor will cause early dielectric failure. Measures commonly employed to prevent well fluids from getting into the motor include the use of elastomeric bladders as well as labyrinth style chambers to isolate the well fluid from the clean dielectric motor fluid. Multiple mechanical shaft seals keep the well fluid from leaking down the shaft. The elastomeric bladder provides a positive barrier to the well fluid. The labyrinth chambers provide fluid separation based on the difference in densities between well fluid and motor oil. Any well fluid that gets past the upper shaft seals or the top chamber is contained in the lower labyrinth chambers as a secondary protection means.
One problem with the use of an elastomeric bladder is that, in high temperature applications, elastomeric bladders may experience a short usable life or may not be suitable for use. Elastomeric materials having a higher temperature tolerance tend to be very expensive. An alternative is to replace the elastomeric bladder with a bellows made of metal or another material that may expand as necessary, but which is suitable for use in high temperature applications, and/or which provide improved reliability over an elastomeric bladder.
Bellows have been used previously in submersible pump applications and other pumping systems. For example, the use of bellows is taught in U.S. Pat. Nos. 2,423,436, 6,059,539, and 6,242,829. Previous use of bellows in an ESP has required that the bellows be placed in an awkward configuration, e.g., as taught in U.S. Pat. No. 2,423,436, or that the bellows be located below the motor in an ESP to avoid interfering with a shaft that traverses the length of the ESP to deliver power from the motor to the pump.
It is desirable to be able to use a bellows to replace an elastomeric expansion bag, and that the bellows be configured in a similar manner to the more commonly used elastomeric expansion bag.